Method for producing flat solution heat treated titanium and zirconium alloy sheets



United States Patent Gfiice 2,836,527 Patented May 27, 1958 lWETI-IODFOR PRODUCENG FLAT SOLUTION HEAT TREATED TITANIUM AND ZIRCONIUM ALLOYSHEETS Harold D. Kessler, Las Vegas, and Raymond S. Richards,

Henderson, New, assignors to Titanium Metals Corporation of America, NewYork, N. Y., a corporation of Pennsylvania No Drawing. ApplicationFebruary 7, 1956 Serial No. 563,836

3 Claims. (Cl. 148-10) This invention relates to the heat treatment ofmetal sheets, and more particularly to solution heat treatment of sheetsof refractory metals such as titanium and zirconium.

Heat treatment of metal sheets is employed to impart specific anddesirable properties thereto. heat treatment the temperature of thesheet is raised sufiiciently to insure solution of certain alloyconstituents, and the heating is generally followed by rapid coolingsuch as quenching. Such sequence of steps often results in distortion ofthe sheet so that it is no longer flat andmakes necessary an additionalstraightening operation to provide heat treated sheet in flat, usefulform.

A principal object of this invention is to provide a simple, economicaland rapid method for solution heat treating metal sheets. A furtherobject'is to provide a method which will produce flat, solution heattreated metal sheets of refractory metals such as titanium andZirconium. Another object is to provide a method for producing fiat,solution heat treated metal sheets in which scaling of the sheet surfaceis materially reduced. A still further object is to provide a rapid,combined method for flattening and solution heat treating metal sheets.These and other obiects of this invention will be apparent from thefollowing detailed description thereof.

This invention, in its broadest aspects, contemplates a method forproducing flat, solution heat treated sheets of metals such as titaniumand zirconium in which the sheet is heated to the required temperatureby passage of an electric current therethrough. During heating the sheetis maintained in a frame or other apparatus, preferably by clamping totwo opposed edges. The clamps, suitably insulated, may serve aselectrodes to conduct electric current through the sheet and also togrip the edges thereof for application of tension to stretch the sheetduring the time it is at elevated temperature, thereby to insureflatness. After the sheet is at the desired temperature and has beenstretched, it is then cooled, preferably quenched, for instance bytreatment with water or brine sprays, and while quenching the sheet ismaintained under tension so that contraction due to cooling will notresult in distortion.

The tension maintained during quenching will generally be less than theyield strength of the sheet.

The method of this invention is particularly adapted to treatment oftitanium and zirconium alloy sheets which have a relatively highelectrical resistance. Such sheets may be of thickness from about 0.005inch to about 0.2 inch. Since the method involves a straighteningoperation, it is not necessary that the original sheet be fiat. Thesheet is held by clamps or jaws engaging opposing edges, preferably theends, and the clamps maintain the sheet in suitable apparatus, which inand of itself forms no part of this invention, adapted to supplyelectric current to pass through the sheet and also to apply tension tothe sheet between the clamps. The electrical and mechanical features ofthe apparatus may be of any suitable type to produce these effects, andmay vary considerably depend- In a solution ing on the size, thicknessand composition of the sheet to be treated, as Well as other factorswhich will be obvious to those skilled in the art.

Sufiicient electric current should be passed through the sheet to heatit rapidly to the required solution heat treatment temperature. Thistemperature will vary according to the composition of the alloy and theproperties desired, but will generally lie within the range of 1300 to1800 F. The sheet is maintained at solution heat treatment temperaturefor a short time to insure proper solution effect. However, this timeshould not be excessivel long, preferably not more than one minute andgenerally not more than ten minutes. Holding the sheet at solution heattreatment temperature longer than about ten minutes to to be avoidedsince this will result in heavy scale formation, which is not readilyremoved and which becomes a serious problem.

The sheet is stretched while it is at solution heat treatmenttemperature. The stretching is preferably accomplished towards the endof the period at which the sheet is maintained at such temperature. Thesheet is stretched to eliminate unfiatness originally in the sheet, orcaused by distortion during the heating step. Preferably the sheet isstretched longitudinally to an extent not more than about 5% of itsoriginal length. Elongation of 5% will be found to remove even grossunflatness, and less elongation may be employed when the condition ofthe sheet needs only a lesser amount to provide substantial flatness.

After stretching the sheet is rapidly cooled; preferably quenched byapplication of water sprays or other equivalent heat extracting means,which may include brine, cooled brine, and high velocity gases. Duringquenching the sheet is maintained under tension to prevent sagging ordistortion due to the quenching operation, but the tension at this stageis suiiicient only to maintain the sheet flatness previously obtainedand no additional stretching is necessary or desirable. Therefore, thetension maintained on the sheet during quenching should generally beless than the yield strength of the sheet, and preferably it will besubstantially less. it may occur, primarily because of nonuniformquenching, that a slight additional stretching may be required duringquenching. Under these conditions the tensile force applied at timesduring quenching may slightly exceed the yield strength of the sheet.The amount of work performed on the sheet should, however, be kept at "aminimum at this stage. Since the sheet will contract during cooling, thetension maintaining apparatus should include hydrauli controls or springmechanisms to provide tensile relief to prevent contraction fromincreasing the force applied above that necessary or desirable. Thequenched sheet will be found to be uniformly solution heat treated,fiat, and lightly scaled so that a simple, aqueous scale remover applied at relatively low temperature will restore an acceptable surfacecondition.

Flatne'ss in metal sheet products of the type to which this inventionrelates, is generally measured as a percentage figure obtained byplacing a straight edge in any direction on the sheet and measuring thelength between contact points and the distance from the straight edge tothe material at the point of greatest deviation. The relation of thedeviation expressed as a percentage of the distance between contactpoints is considered flatness. Since flatness is a relative quality, itwill vary somewhat according to the use requirements and other factors.Specifications often call for flatness not exceeding two or threepercent for some applications, while for other uses a seven or eightpercent flatness maybe acceptable. Often rolled products Withoutstraightening will show a serious unjiatness determined as high as 15%or higher flatness.

'to the sheet maintained by the clamps. direct currentele'ctric powerwas connected'to each of .formability inevitably result.

i The followingexample will illustrate the practice of an e b d en of te ion.

Example 1 'An unflattened sheet (flatness 16% ZOinches by 30 inches;rolled from a titanium basef alloy'containing 6% aluminum and 4%vauadiumand of thickness .075" was clamped securely in a frame by itsend edges. "One end of'the frame and its associated clamp was arrangedto be movable with respect to the opposite clamp, and arranged to be'actuated by a hydraulic cylinder to apply tension A source of theclamps, which were insulated from the rest of the structure, and acurrent of 14,000 amperes and 10 volts was applied to the sheet. 'Thetemperature of the sheet was thereby raised to 1550" F. in about 30seconds. On reaching this. temperaturethe power source was cut back tol0,000 amperes tomaintain'the sheet at 1550 for two minutes.Stretching'was initiated just prior to the endof the two minute holdingperiod by application of a tensile force of 4,000 pounds. between theclamps until anelongation of 3%'in the length of the sheet was obtained.At this stage the sheet was essentially flat. The electric heatingcurrent was then turned oil and simultaneously water sprays were appliedto quench the sheet. At the same time a relief valve in the hydrauliccylinder actuating the stretching mechanism perature accomplishesflattening under conditions which do not affect the mechanicalproperties of the sheet. In;

this respect the method of this invention is unique and does notintroduce disadvantageous eiiects such as work 7 hardening which occurswhen stretching is accomplished cold or at moderately elevatedtemperature such as 500 to 700 F. When metal-sheets are worked, as bystretching, at temperatures much below the solution heat treatingtemperature, appreciable and deleterious hardening, increasein' yieldstrength, and reduction in ductility and vention, however, since thedeformation of the sheet is accomplished at solution heat treatmenttemperature,

these disadvantages are not encountered and the mechan- In the method ofthis in agents such as molten alkali applied at temperatures of;

the order of 800 F. or higher. Such treatment is expensive and difiicultto apply to thin sheets and, more.

over, exposure of the solution heat treated and quenched sheet again toa temperature as high as 800 F. or higher results in substantial changein mechanical properties. Since the heat treatment andiflatteningoperation, according to this invention, is carried out in anextremelyshort space of time, never longer than a few minutes; the scale formedunder these conditions is of such character that it maybe're'adilyremoved by anaqueous descaling agent at' temper'atures belowthat at which any deleterious effect on the sheet properties occur.

claim; 1 s L l. A method for producing flat, solution heat treatedsheets of a metal selected from the' group consisting of titanium andzirconium base alloys, which comprises: heating said sheet by passage ofan electric current therethrough until the temperature thereof:reachesibetween 1300 'F. and 1800 F.; maintaining said sheet at saidtemperature of a period not exceeding ten :minutes, stretching saidsheetto provide an elongation thereof of not more than 5% in onedirection during the time that said sheet is maintained at saidtemperature and quencha ing said sheet whilemaintaining it undertension.

2. A methodrfor producing flat, solution heat treated sheets of. a metalselected from the group consisting of titanium and zirconium base alloyswhich comprises: heating said sheet by passage of an electric currenttherethrough until the temperature thereof reachesbetween 1300 F. and1800 F., maintaining said sheet at said temperature for a period notexceeding two;,minutes, stretching said sheet to provide an elongationthereof or not inore'than 5% in one direction towardrthe end of the timethat said sheet is maintained at said temper: ature. and quenching saidsheet while maintaining it under tension. 7 Y

3. A 'method'for producing flat, solution heat treated sheets of a metalselected from the group consisting of titanium and zirconium base alloyswhich comprises;

heating said sheet by passage-of an electric current there: throughuntil the' temperature thereof reaches between 1300 F. and 1800 F.,maintaining said sheet'at said temperature for -a period not exceedingten minutes,-

ical propertiesof the solution heat treated sheet are 'essentially thesame as ifit had not been subjected to any stretching or straighteningwork. p

The ability to heat treatand straighten thin metal sheets in anextremely short period of time is another important featureof thisinvention. Exposure to the atmosphere of alloys of thetype to which thisinvention relates at high temperatures inevitably results in scaling ofthe sheet surface. If the scaling is severe, it cannot 7 not more than5% in one direction during the time that said sheet is maintained atsaid temperature and quench; mg said sheet while maintaining it undertension less than its yield strength.

References Cited the file of this patent V I UNITED STATES PATENTS OTHERREFERENCES V w. A. D. 0. Technical Report 53-26, April 1953,

vestigation of Heat Treatment of Commercial Titanium Base Alloys, page6.

1. A METHOD FOR PRODUCING FLAT, SOLUTION HEAT TREATED SHEETS OF A METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM BASE ALLOYS WHICH COMPRISES: HEATING SAID SHEET BY PASSAGE OF AN ELECTRIC CURRENT THERETHROUGH UNTIL THE TEMPERATURE THEREOF REACHES BETWEEN 1300*F. AND 1800*F., MAINTAINING SAID SHEET AT SAID TEMPERATURE OF A PERIOD NOT EXCEEDING TEN MINUTES, STRETCHING SAID SHEET TO PROVIDE AN ELONGATION THEREOF OF NOT MORE THAN 5% IN ONE DIRECTION DURING THE TIME THAT SAID SHEET IS MAINTAINED AT SAID TEMPERATURE AND QUENCHING SAID SHEET WHILE MAINTAINING IT UNDER TENSION. 